Doc Savage and The Shadow are mentioned in the fictional "Under the Hood" segment at the end of Watchmen #1
The world of Doc
Savage and The Shadow was one
of absolute values, where what
was good was never in the slight-
est doubt and where what was
evil inevitably suffered some fit-
Action Comics #1 also gets a mention. Note that Superman, Zatara, Doc Savage and the Shadow are all explicitly called out as examples of fictional superheroes whose star waned once there were stories about real superheroes like Ozymandias and Captain Metropolis.
For me, it all started in 1938, the year when they invented the super-hero. I was too old
for comic books when the first issue of ACTION COMICS came out, or at least too old to read
them in public without souring my promotion chances, but I noticed a lot of the little kids on
my beat reading it and couldn’t resist asking one of them if I could glance through it. I figured if anybody saw me I could put it all down to keeping a good relationship with the youth of the community.
I’d never been entirely sure what
Lamont Cranston was up to with Margo Lane, but I’d bet it was nowhere near as innocent and
wholesome as Clark Kent’s relationship with her namesake Lois. Of course, all of these old
Characters are gone and forgotten now, but I’m willing to bet that there are at least a few older readers out there who will remember enough to know what I’m talking about.
Superman and The Flash (erroneously referred to as Flash-Man) get a mention in Watchmen #3
Mr Spock gets a mention in Watchmen #9.